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...import hooks to work, the module or package must be physically located under its new name. This is because the import hooks catch only modules that are not already imported, and cannot be imported by Python's built-in import rules. Thus, if a module has been moved, say from Lib/StringIO.py to Lib/stringio.py, and the former's .pyc file has been removed, then without the remapper, this would fail: import StringIO Instead, with the remapper, this failing import will be caught, the old name wil...
...import importlib.machinery import importlib.util loader = importlib.machinery.ExtensionFileLoader(name, path) spec = importlib.util.spec_from_loader(name, loader) module = importlib.util.module_from_spec(spec) loader.exec_module(module) return module On platforms that support symbolic links, these may be used to install one library under multiple names, exposing all exported modules to normal import machinery. Testing and initial implementations For testing, a new built-in module _testmultiph...
...import name that sounds overly generic but in practice was obvious to users as to what it does: from __future__ import division Prior discussion In PEP 484 The forward reference problem was discussed when PEP 484 was originally drafted, leading to the following statement in the document: A compromise is possible where a __future__ import could enable turning all annotations in a given module into string literals, as follows: from __future__ import annotations class ImSet: def add(se...
...import cleanup - when a module import failed, versions of Python prior to 2.4a2 would leave a broken module in sys.modules - subsequent attempts to import the failing module would silently succeed, but use the broken module object. The import machinery now removes the failing module from sys.modules if the import fails. The -m command line option - python -m modulename will find a module in the standard library, and invoke it. For example, python -m pdb is equivalent to python /usr/lib/python...
...ImportError when asked to import foo. In other words, Python will not import a pyc file from the cache directory unless the source file exists. Case 4: legacy pyc files and source-less imports Python will ignore all legacy pyc files when a source file exists next to it. In other words, if a foo.pyc file exists next to the foo.py file, the pyc file will be ignored in all cases In order to continue to support source-less distributions though, if the source file is missing, Python will import a...
...Imports Imports should usually be on separate lines: # Correct: import os import sys # Wrong: import sys, os It's okay to say this though: # Correct: from subprocess import Popen, PIPE Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants. Imports should be grouped in the following order: Standard library imports. Related third party imports. Local application/library specific imports. You should put a blan...
...Imports In Python 3, implicit relative imports within packages are no longer available - only absolute imports and explicit relative imports are supported. In addition, star imports (e.g. from x import *) are only permitted in module level code. Also, some areas of the standard library have been reorganized to make the naming scheme more intuitive. Some rarely used builtins have been relocated to standard library modules. Iterators and views Many APIs, which in Python 2 returned concrete list...
...import one of the missing modules, Python will fail with a ModuleNotFoundError. For example, after deliberately removing sqlite-devel from the local system: $ ./python -c "import sqlite3" Traceback (most recent call last): File "<string>", line 1, in <module> File "/home/ncoghlan/devel/cpython/Lib/sqlite3/__init__.py", line 23, in <module> from sqlite3.dbapi2 import * File "/home/ncoghlan/devel/cpython/Lib/sqlite3/dbapi2.py", line 27, in <module> from _sqli...
...imports work in Python, it is often not possible to import all the needed models directly: # File models/a.py from models.b import B class A(Model): def foo(self, b: B): ... # File models/b.py from models.a import A class B(Model): def bar(self, a: A): ... # File main.py from models.a import A from models.b import B Assuming main is imported first, this will fail with an ImportError at the line from models.a import A in models/b.py, which is being imported from models/a.py before a h...
...import and execution functionality involving code from a file will be changed to use open_code() unconditionally. It is important to note that calls to compile(), exec() and eval() do not go through this function - an audit hook that includes the code from these calls is the best opportunity to validate code that is read from the file. Given the current decoupling between import and execution in Python, most imported code will go through both open_code() and the log hook for compile, and so care...
...import one module, distutils.core. This module is responsible for parsing all command-line arguments to setup.py (even though the interpretation of options is distributed across the various Distutils commands, and possibly the client setup.py). It also takes care of receiving control from setup.py, and passing it as appropriate to Distutils commands. Most importantly, distutils.core defines the Distribution class, which is the heart and soul of the ...
Import Sig Introduction PEP 382 (namespace packages) and to perform any additional import.c and importlib refactoring that would be useful to this cause. The intent is that this SIG will be re-retired after Python 3.3 is released.
...importlib, a fully import-hook based import system implementation PEP 3147's change in the bytecode cache layout to use __pycache__ subdirectories, including the source_to_cache(path) and cache_to_source(path) APIs that allow the interpreter to automatically handle the redirection to a separate cache directory Abstract This PEP outlines a mechanism for controlling the generation and location of compiled Python bytecode files. This idea originally arose as a patch request [1] and evolved into...
...imported for the first time, python compiles the bytecode and runs the binding optimization. Subsequent imports just re-use the previous work. Each session repeats this process (the results are not saved in pyc files). How do you know this works? I implemented it, applied it to every module in library, and the test suite ran without exception. What if the module defines a variable shadowing a builtin? This does happen. For instance, True can be redefined at the module level as True = (1==1)...
...important design criteria. Algorithms, energy terms, and specializations of the data types can be added without having to modify the MMTK code. The design of MMTK as a library, rather than a closed program, is essential for many applications. An important aspect of biomolecular simulations is visualization. MMTK delegates this task to external tools. Two visualization programs, VMD and PyMOL, are particularly well integrated. Most MMTK users access the library from simple Python scripts, but MMT...
...imported, and that's unacceptable. Tests Fixed the pickle tests to work with "import test.test_pickle". Tweaked test_locale.py to actually run the test Windows. In distutils/archive_util.py, call zipfile.ZipFile() with mode "w", not "wb" (which is not a valid mode at all). Fix pstats browser crashes. Import readline if it exists to make the user interface nicer. Add "import thread" to the top of test modules that import the threading module (test_asynch...
...import bzrlib >>> bzrlib.__version__ '2.3.0' Retrieving the version number from a standard library package that is also distributed as a standalone module: >>> import email >>> email.__version__ '5.1.0' Version numbers for namespace packages: >>> import flufl.i18n >>> import flufl.enum >>> import flufl.lock >>> print flufl.i18n.__version__ 1.0.4 >>> print flufl.enum.__version__ 3.1 >>> print flufl.lock.__versio...
...important. Most computers, however, will be incorporated into something else, rather than standing alone. This process has already begun. Automobiles employ multiple embedded systems, some of which communicate with each other. Embedded systems also operate many household appliances. Such systems are likewise very important in industry, where they form a crucial element of many instruments and tools. The catalyst for the future expansion of embedded systems is the rapid advance of network te...
...import os, sys ... #!/usr/bin/python # -*- coding: iso-8859-15 -*- import os, sys ... #!/usr/bin/python # -*- coding: ascii -*- import os, sys ... Without interpreter line, using plain text: # This Python file uses the following encoding: utf-8 import os, sys ... Text editors might have different ways of defining the file's encoding, e.g.: #!/usr/local/bin/python # coding: latin-1 import os, sys ... Without encoding comment, Python's parser will assume ASCII text: #!/usr/local/bin/pyt...